The present invention relates to collapsible truss structures usable for a wide variety of applications. An important application is that to medium to large structures to be placed in outer space. Principal examples of such structures are large antenna structures, solar power-generation satellites, space colonies, space factories, and space bases or stations. The collapsible structures according to the present invention can also be used on earth. One example of such structures is a temporary structure of portable type for emergency use.
In general, a space structure is transported into outer space as a payload of a rocket-propelled spacecraft such as a space shuttle. A payload is restricted in bulk volume and weight by the capacity of a rocket used for lift-off. For this reason it is necessary to make the payload structure as small and as light as possible. A representative form of space structures of medium to large size is that of truss construction. Truss structures are advantageously light but are disadvantageously restricted by their bulk volume in many cases.
In view of this circumstance, expandible-collapsible structures are being observed with great interest as a promising form of space structure. The structures are highly advantageous in that, at the time of lift-off, the bulk volume occupied by the structure can be greatly reduced by being folded or collapsed. Then, upon reaching their space destination, the structures are unfolded or expanded to assume their final form.
Generally, a one-dimensional truss construction has a wide range of applications to space structures such as keel beams of space stations and large antenna booms.
A typical example of expandible-collapsible structures of this nature is a box truss of the Martin Marietta corporation. Concerning this truss, a description is set forth in the following publication.
Herbert, J. J. et al., "Technology Needs of Advanced Earth Observation Spacecraft", NASA CP-3698, Jan. 1984.
The box truss, similarly as in many other one-dimensional expandible-collapsible structures, is adapted to be collapsed by pivotally flexing each skeletal member at a geniculate or knee joint provided at a middle part of the skeletal member.
In the truss construction of this character, there is a weakness in the middle part of each member, which has the largest effect on the Euler buckling. For this reason the construction is disadvantageous because of inadequate rigidity of the structure. Lowering of the rigidity is prevented by using a strong locking mechanism at each joint. However this measure would increase weight.
Another problem arises from the need to expand the structure automatically or semiautomatically in outer space. For this purpose, high reliability of the pertinent mechanisms is required. While a small number of locking mechanisms is desirable, four locking mechanisms are necessary for each basic unit in the above described truss. This is not desirable.
Accordingly, in order to solve the above described problems, there has been proposed a truss construction which has a minimal number of locking mechanisms for the joint and moreover has large rigidity and light weight. This truss construction is disclosed in U.S. Pat. No. 4,771,585 issued Sep. 20, 1988.
However, even this truss structure is not fully satisfactory on the points of number of locking mechanisms, strength, and weight.